As others have said, there are two whistle/horn positions. I find my modern electronics are most reliable with moving the control half way on a ZW.
That is the "pickup" position. The whistle control was never meant to be left in that position, which puts the full load through the rectifier. When in the "holding" position, a resistor is placed in parallel with the rectifier, sharing the load.
Is using the whistle control in such a fashion problematic? ----- I don't know.
